Tank for storing a reducing agent

ABSTRACT

The invention relates to a tank for storing a reducing agent, in particular a liquid reducing agent for reducing nitrogen oxides from the waste gas of an internal combustion engine to nitrogen and water. The tank includes an external container in which an internal container is accommodated. The internal container is held in the external container in a mounting that can be axially displaced in relation to an axis of the external container. The internal container is held such that the volume in the external container is modified by displacing the internal container in the mounting.

PRIOR ART

The invention relates to a tank for storing a liquid reducing agent according to the preamble to claim 1.

In internal combustion engines, particularly in diesel-operated internal combustion engines, due to stricter exhaust legislation going into effect in the next few years, it will be necessary among other things to reduce the percentage of nitrogen oxides in exhaust. In order to reduce the percentage of nitrogen oxides, a selective catalytic reduction, for example, is carried out in which the nitrogen oxides are reduced to nitrogen and water with the aid of reducing agents. For example, an aqueous urea solution is used as a reducing agent.

The reducing agent is normally stored in a tank and supplied via a line from the tank to a metering module that injects the reducing agent into the exhaust pipe, for example.

Depending on the antifreeze used, the conventional liquid reducing agents currently in use freeze at a temperature in the range from −11° C. to −40° C. The phase shift from the liquid aggregate state into the solid aggregate state causes the reducing agent to undergo a volume expansion of approximately 7%. In order to prevent the tank from bursting due to the freezing of the reducing agent, in the tanks currently in use for storing reducing agent, the tank is not completely filled so that if freezing occurs, there is always an air cushion above the reducing agent.

The presence of this air cushion produces a thermal insulation of the reducing agent at the top of the tank. The freezing of the reducing agent consequently begins at the sides and the bottom. The volume expansion of the freezing liquid consequently always occurs in the direction toward the air space in the tank, toward the middle of the tank. As a result, the reducing agent causes a dome to form as it freezes. The presence of the air cushion prevents the tank from being damaged when the reducing agent freezes.

A disadvantage of the air cushion in the tank, however, is that if the tank is overfilled, an expansion of the reducing agent can cause damage to the tank.

DISCLOSURE OF THE INVENTION Advantages of the Invention

A tank embodied according to the invention for storing a reducing agent, in particular a liquid reducing agent for reducing nitrogen oxides in the exhaust of an internal combustion engine to nitrogen and water, includes an outer container in which an inner container is accommodated. The inner container is accommodated in the outer container in a mount that is able to slide in relation to an axis of the outer container, the inner container being supported so that a sliding of the inner container in the mount changes the volume of the outer container.

An advantage of the tank according to the invention is that a deformation of the outer container during the freezing of the reducing agent leads to a shifting of the wall of the outer container without a shifting of the inner container, enlarging the volume in the outer container. The fixed positioning of the inner container avoids damage that can occur if the position of the inner container changes. Such damage can include, for example, the bending or rupturing of fixed connections or rigid lines with which the inner container is attached, for example, to a vehicle body.

In one embodiment, a spring element is accommodated between the inner container and the outer container. The spring element permits the inner container to be axially fixed in relation to the outer container. Through the use of a spring element, however, it remains possible for the inner container to slide in an axial direction in the outer container. The spring element preferably rests with one end against the bottom of the inner container and rests with the other end against the bottom of the outer container. The spring element, which is accommodated between the inner container and the outer container, is preferably manufactured out of elastomer.

In order for the volume of the outer container to increase due to the sliding of the inner container, it is preferable for the inner container to be accommodated in an opening in the outer container in such a way that the inner container protrudes from the outer container. If the inner container were completely enclosed by the outer container, then a sliding of the inner container would only result in a geometrical change of the volume of the outer container, but the volume would remain the same size.

In order to attach the inner container to the outer container, the inner container is preferably embodied with a shoulder that is acted on by a coupling element, which is attached to the outer container with either frictional, nonpositive engagement or form-locked engagement. A suitable coupling element, for example, is a coupling nut that is screwed onto a thread encompassing the inner container.

In order to permit the inner container to slide axially when it is fastened to the outer container with the aid of the coupling element, preferably an elastic sealing ring is accommodated between the inner container and the outer container, in the region of the axial mount at which the inner container protrudes from the outer container. In this instance, the elastic sealing ring rests, for example, on the shoulder of the inner container while the outer container rests against the opposite side of the elastic sealing ring. As soon as the reducing agent freezes and the volume of the reducing agent increases as a result, the wall of the outer container is moved upward along the inner container due to the volume increase of the reducing agent while the coupling element lifts up from the sealing ring. The elastic sealing ring in this case preferably expands in order to assure the tightness of the seal. Another purpose of the elastic sealing ring is to provide a seal that protects the connection between the outer container and the inner container from the surrounding environment so that no reducing agent can escape from the outer container. This is particularly necessary when the reducing agent in the outer container is not frozen.

The inner container is preferably connected to a supply module. The connection of the supply module to the inner container is preferably embodied so as to prevent a relative movement between the supply module and the inner container. To this end, the supply module is preferably placed directly onto the inner container. The supply module generally includes a pump with which reducing agent can be drawn from the inner container.

The inner container preferably also accommodates a heating element that can be used to thaw frozen reducing agent. The heating element is preferably also connected to the supply module and is triggered by means of the supply module. Attaching the supply module to the inner container so as to prevent a relative movement between the inner container and the supply module also prevents damage to the heating element that would occur if the supply module were to move in relation to the inner container as soon as the reducing agent in the inner container froze solid. The relative movement between the supply module and inner container would occur, for example, because the freezing of the reducing agent would push against the supply module and lift it from the inner container if a sufficient attachment were not provided. Since the heating element is generally rigidly connected to the supply module and is no longer mobile due to the frozen reducing agent in the inner container, this might possibly cause the heating element to be torn out from the supply module. A heating would no longer be possible, thus rendering it no longer possible to thaw the reducing agent. In general, the tank is constructed so that the supply module connected to the inner container is positioned outside the outer container. The positioning of the supply module outside the outer container makes it possible, for example in the event of damage to the supply module, to simply repair and replace the supply module without having to disassemble the entire tank.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are shown in the drawings and explained in greater detail in the following description.

Drawings

FIG. 1 shows a tank for storing reducing agent in which the reducing agent is frozen,

FIG. 2 is a schematic depiction of a tank embodied according to the invention for storing a reducing agent,

FIG. 3 is a detailed depiction of an attachment of an inner container in an outer container with a coupling element.

EMBODIMENTS OF THE INVENTION

FIG. 1 shows a tank for storing a reducing agent. A tank 1 includes an outer container 3 in which an inner container 5 is accommodated. The inner container 5 is fastened to the outer container 3, for example by means of a coupling element. A suitable coupling element is a coupling nut, for example. It is also conceivable, however to use any other fastening option known to those skilled in the art. The inner container 5 is attached to a supply module 7. For example, the supply module 7 includes a supply pump with which reducing agent can be supplied from the inner container 5. The supply module 7 is also connected to a heating element 9. The heating element 9 can be used to thaw the reducing agent in the inner container 5 when it is frozen. The heating element is preferably embodied so that it encompasses a supply line 11. The fact that the supply line 11 is encompassed by the heating element 9 means that frozen reducing agent that is contained in the supply line 11 is thawed first. The supply line 11 is connected to the supply pump 13 contained in the supply module 7. The supply pump 13 is connected to a reducing agent line 15. The reducing agent line 15 ends at a metering device 17 that supplies the liquid reducing agent to an SCR (selective catalytic reduction) catalytic converter, which is not depicted here. Nitrogen oxides, which are produced during the combustion of fuel in an internal combustion engine and are conveyed out with the exhaust, are reduced to nitrogen and water in the SCR catalytic converter. The reducing agent, for example, is an aqueous urea solution.

In the hot exhaust, the liquid reducing agent evaporates and forms ammonia that is deposited in the SCR catalytic converter. The nitrogen oxides contained in the exhaust are converted into elementary nitrogen and water vapor by the ammonia that is deposited in the SCR catalytic converter.

At temperatures below its melting point, the liquid reducing agent freezes. The freezing process begins at the walls of the outer container 3 and continues on into the interior of the outer container 3. When an aqueous urea solution is used as a liquid reducing agent, it freezes at a temperature between −11° C. and −40° C. The temperature depends on which antifreeze or how much antifreeze has been added to the liquid reducing agent. It generally takes several days for the reducing agent to freeze completely. The volume expansion of the reducing agent as it freezes causes a dome 19 to form. Since the freezing process begins at the walls of the outer container 3 and continues on into the interior, the dome 19 encompasses the inner container 5. The frozen reducing agent in the outer container is labeled with the reference numeral 21 in FIG. 1.

So that the formation of the dome 19 does not destroy the outer container 3, the outer container 3 is only filled to a level that leaves an air space 23 above the reducing agent. The formation of the dome 19 displaces air from the air space 23. The size of the air space 23 is selected to be large enough to avoid a deformation of the outer container 3, even when the reducing agent 21 is completely frozen. The volume taken up by the air space 23 is at least equal to the volume by which the reducing agent expands when it freezes.

After the reducing agent in the outer container 3 has frozen to the point that the frozen reducing agent 21 contacts the wall 25 of the inner container 5, the reducing agent in the inner container 5 also begins to freeze. In the inner container 5 as well, the freezing process begins at the wall 25 and continues on toward the middle of the inner container 5. In the embodiment show in FIG. 1, a part of the reducing agent inside the inner container 5 is already frozen. This frozen reducing agent in the inner container is labeled with the reference numeral 27. Since the reducing agent is not yet completely frozen, the inner container 5 also contains liquid reducing agent 29. Since the freezing process begins at the walls 25 of the inner container 5, the frozen reducing agent 27 encompasses the liquid reducing agent 29. When the liquid reducing agent 29 in the inner container 5 freezes further, the phase boundary 31 between the frozen reducing agent 27 and the liquid reducing agent 29 moves further upward and toward the center. The volume expansion of the reducing agent then causes a dome to also form in the inner container 5. For this reason, it is likewise necessary for the inner container 5 to contain an air cushion 33 in order to avoid damage to the inner container. So that the freezing of the reducing agent in the inner container 5 does not damage the heating element 5, the inner container 5 is preferably rigidly connected to the supply module 7.

The inner container 5 in this case is rigidly connected to the outer container 3. It is not possible for the inner container 5 to move in the outer container 3. If the outer container is overfilled and the air cushion 23 is too small, then the frozen reducing agent pushes the wall of the outer container 3 outward. This can damage the outer container 3.

FIG. 2 shows a tank embodied according to the invention, with an axially sliding inner container.

A tank 1 embodied according to the invention likewise includes an inner container 5 that is accommodated in an outer container 3. The inner container 5 is connected to the supply module 7 so as to form a functional unit. The connection of the inner container 5 to the supply module 7 is known to those skilled in the art and is therefore depicted only schematically here.

According to the invention, the inner container 5 is accommodated in the outer container in an axial mount 35 that is able to slide in relation to an axis 37 in the outer container 3. As soon as the reducing agent in the outer container 3 freezes and therefore expands, the inner container 5 that is attached to the supply module 7 to form the functional unit is pushed out of the inner container 3 in the axial direction. This avoids damage to the outer container 3 when the reducing agent freezes, even if the outer container 3 is overfilled, thus leaving an insufficient air cushion.

Any mount known to those skilled in the art is suitable for use as the axially movable mount 35. In order to prevent the inner container 5 from starting to move inside the outer container 3, e.g. due to externally exerted forces, the inner container 5 is elastically attached to the outer container 3. The attachment of the inner container 5 to the outer container 3 is carried out, for example as shown in FIG. 2, by means of a spring element 39, which is accommodated between the bottom 41 of the inner container 5 and the bottom 43 of the outer container 3. In order to prevent the inner container 5 from starting to oscillate, it is necessary for the spring element 39 to have a sufficiently high spring constant. A suitable spring element 39, for example, is a cushion composed of an elastomer.

Movements of the inner container 5 in the outer container 3 are induced, for example, when the tank 1 embodied according to the invention is used in a motor vehicle. As soon as the motor vehicle is driven, irregularities in the road surface are transmitted to the motor vehicle and therefore also to the tank 1. Because of the differing masses of the outer container 3 and inner container 5, these are accelerated differently so that the movements of the vehicle cause a relative movement between the outer container 3 and the inner container 5. The spring element 39 reduces or preferably completely eliminates this relative movement between the inner container 5 and the outer container 3.

The axially movable mount 35 is preferably embodied so that it is fluid-tight. This prevents liquid reducing agent from being able to escape from the outer container 3 into the environment.

FIG. 3 shows an example of an axially movable mount.

In the embodiment shown in FIG. 3, the functional unit 45 including the inner container 5 and the supply module 7 is fastened to the outer container 3 with a coupling element 47. To this end, the outer container 3 is provided with a sleeve-shaped extension 49 on which an external thread 51 is embodied. The sleeve-shaped extension 49 encompasses an opening 54 into which the functional unit 45 is inserted. In order to secure the functional unit 45 in the outer container 3, a shoulder 53 is embodied on the functional unit 45. The coupling element 47, which in this case is embodied in the form of a coupling nut and is screwed onto the external thread 51 on the sleeve-shaped extension 49, acts on the shoulder 53 and secures the functional unit 45 in the outer container 3. In order to produce a seal, an elastic sealing element 55 is accommodated between the sleeve-shaped extension 49 and the functional unit 45. Preferably, the sealing element 55 is profiled. Because of the profiling, the sealing element 55 is radially elastic. The sealing element 55 is mounted between the sleeve-shaped extension 49 and the functional unit 45 with a moderate amount of radial prestressing. On the one hand, this permits the functional unit 45 to slide axially in the outer container 3 in relation to the axis 37 and on the other hand, this also provides a seal between the functional unit 45 and the outer container 3 so that no reducing agent can escape from the outer container 3 into the environment.

In a preferred embodiment, the sealing element 55 has a collar 57 that rests against the shoulder 53, thus assuring an additional axial seal. To permit an axial sliding of the functional unit 45 in the outer container 3, though, it is necessary for the collar 57 to be very elastic. This can be assured, for example, by means of an intense profiling. Another purpose of the collar 57 is to axially position the sealing element 55 in the axially movable mount 35 that is composed of the sleeve-shaped extension 49 and the functional unit 45 accommodated therein. A sufficiently large distance between the shoulder 53 and the coupling element 47 is achieved by the fact that the coupling element 47 is placed against a stop 59. The stop 59 is embodied, for example, as an end surface on the sleeve-shaped extension 49.

The spring element 39, which in the embodiment shown here is embodied as an elastomer part, prevents the functional unit 45 from falling into the outer container 3 until it rests against the bottom of the outer container 3. The spring element 39 establishes a distance between the bottom 41 of the inner container 5 and the bottom 43 of the outer container 3. The height of the spring element 39 also establishes the distance between the shoulder 53 and the coupling element 47.

If the reducing agent in the outer container 3 then begins to freeze, a force is exerted on the outer container 3. This is depicted by the arrows 61. The force 61 acting on the outer container 3 causes the casing of the outer container 3 to be pushed outward. This upward-directed deformation can be absorbed by the axially movable mount 35, thus preventing a damage to the tank 1. Even when a deformation of the casing of the outer container 3 occurs, the functional unit 45 remains in its position. As a result no strain is exerted on lines and devices connecting the functional unit 45 to a vehicle body, for example. It is also not a problem if the coupling element 47 lifts away from the collar 57 of the sealing element 55 because it is not necessary for a seal to prevent the escape of liquid if the reducing agent in the outer container 3 is frozen. As soon as the reducing agent has thawed again, the coupling element 47 drops back down onto the collar 57 and the collar 57 produces the axial seal once more. The spring element 39 can also hold the functional unit 45 in its position if the bottom 43 of the outer container 3 moves in relation to the functional unit 45. With a rigid connection of the functional unit 45 to the bottom 43 of the outer container 3, the functional unit 45 would move in relation to the vehicle body and this could result in damage. 

1-10. (canceled)
 11. A tank for storing a reducing agent, in particular a liquid reducing agent for reducing nitrogen oxides in the exhaust of an internal combustion engine to nitrogen and water, comprising: an outer container; an inner container accommodated within the inner container; a mount supporting the inner container within the outer container, wherein the mount is able to slide axially in relation to an axis of the outer container, and the inner container is supported so that a sliding of the inner container in the mount changes the volume of the outer container.
 12. The tank as recited in claim 11, wherein a spring element is disposed between the inner container and the outer container.
 13. The tail as recited in claim 12, wherein the spring element rests with one end against a bottom of the inner container and rests with an other end against a bottom of the outer container.
 14. The tank as recited in claim 12, wherein the spring element is manufactured out of an elastomer.
 15. The tank as recited in claim 13, wherein the spring element is manufactured out of an elastomer.
 16. The tank as recited in claim 11, wherein the inner container is accommodated in an opening of the outer container in such a way that the inner container protrudes from the outer container.
 17. The tank as recited in claim 12, wherein the inner container is accommodated in an opening of the outer container in such a way that the inner container protrudes from the outer container.
 18. The tank as recited in claim 13, wherein the inner container is accommodated in an opening of the outer container in such a way that the inner container protrudes from the outer container.
 19. The tank as recited in claim 14, wherein the inner container is accommodated in an opening of the outer container in such a way that the inner container protrudes from the outer container.
 20. The tank as recited in claim 15, wherein the inner container is accommodated in an opening of the outer container in such a way that the inner container protrudes from the outer container.
 21. The tank as recited in claim 11, wherein the inner container is embodied with a shoulder that is acted on by a coupling element, which coupling element is attached to the outer container with either frictional, nonpositive engagement or form-locked engagement.
 22. The tank as recited in claim 12, wherein the inner container is embodied with a shoulder that is acted on by a coupling element, which coupling element is attached to the outer container with either frictional, nonpositive engagement or form-locked engagement.
 23. The tank as recited in claim 15, wherein the inner container is embodied with a shoulder that is acted on by a coupling element, which coupling element is attached to the outer container with either frictional, nonpositive engagement or form-locked engagement.
 24. The tank as recited in claim 11 wherein an elastic sealing element is accommodated between the inner container and the outer container, in a region of the mount at which the inner container protrudes from the outer container.
 25. The tank as recited in claim 20, wherein an elastic sealing element is accommodated between the inner container and the outer containers in a region of the mount at which the inner container protrudes from the outer container.
 26. The tank as recited in claim 11, wherein the inner container is connected to a supply module.
 27. The tank as recited in claim 25, wherein the inner container is connected to a supply module.
 28. The tank as recited in claim 26, wherein the supply module is connected to the inner container so as to be positioned outside of the outer container.
 29. The tank as recited in claim 27, wherein the supply module is connected to the inner container so as to be positioned outside of the outer container.
 30. The tank as recited in claim 11, wherein a heating element is accommodated in the inner container. 